Add support for tracing

[mattmcf]

Issue
Sometimes ledger API operations take a long time. It's hard to distinguish and measure exactly how much latency accumulates in your app vs. in the ledger vendor's API.

Describe the solution you'd like
I'm wondering if a ledger operation can be enhanced to support or pick up tracing specified by the consuming framework. What would that look like?

For example, we use a rails app that is instrumented with datadog's D-Trace. We get a ton of metrics and interoperability for free.

Alternatives

Would we add support for the open tracing gem? Or what would generic tracing support look like?

Questions

What would the scope of this change look like?

[ryanwjackson]

If helpful, I imagine there is some data on the Faraday request/response object, which is encapsulated and stored in op.perform.response.

But I do agree, some tracing would be nice. I imagine the lib itself has some silly inefficiencies.